There is a big problem with user authentication and payment. The user can login and use internet access without payment - only by choosen a profile. For details:
http://forum.mikrotik.com/t/authenticated-even-with-timed-out-payment/56479/6
The same problem in 6.0.3 (using x86 version - this works fine, without kernel problem and without corrupted um-database)
rg
maxeschm